EFFECTS OF IBMX ON THE ROD ERG OF THE ISOLATED PERFUSED CAT EYE - ANTAGONISM WITH LIGHT, CALCIUM OR L-CIS-DILTIAZEM

Full-field electroretinograms (ERGs) were recorded from isolated cat eyes perfused through the ophthalmociliary artery with the cGMP-PDE inhibitor, 3-isobutylmethylxanthine (IBMX). Under dark-adapted conditions perfusion with IBMX resulted in reduced ERG b-wave amplitudes at low stimulus luminances and supernormal b-wave amplitudes at high stimulus luminances with reduced b-wave sensitivity; b-wave implicit times were more delayed at low than at high stimulus luminances. Presentation of a steady white background or high calcium fully reversed the supernormal amplitudes and partially reversed the delayed implicit times produced by IBMX. Rod ERG b-wave sensitivity, reduced with IBMX alone, was partially reversed with calcium but further reduced with background light. Perfusion with the cation channel blocker, L-cis-diltiazem, also reversed the supernormal amplitudes produced by IBMX but had no effect on implicit times or b-wave sensitivity. Possible mechanisms of action of these antagonists and clinical implications of these findings are considered.